The present invention relates to water purification and, more particularly, to water purification employing a microscreen for filtration.
Hollow, cylindrical microscreens for water filtration are well known in the field of water purification. One such microscreen is disclosed in U.S. Pat. No. 4,038,187 granted to E. Saffran and entitled "Microscreen Drum," the teachings of which are incorporated herein by this reference thereto. However, it will be readily apparent that this invention can also be practiced with microscreens other than that taught by Saffran.
To be commercially useful, a microscreen must be able to pass large quantities of water each day. The rate of flow of water through a microscreen is directly proportional to the pressure head of the water and the microscreen pore size. Thus, if the pressure head is small, the amount of water passing through the microscreen might be inadequate for commercial usage. Conversely, if the pressure head is large, the microscreen might be unable to withstand the pressure and loose its integrity by tearing or rupturing, for example.
Likewise, if the pores of the microscreen are small, the rate of flow through the microscreen might be inadequate for commercial usage. Conversely, if the pores of the microscreen are large enough to insure a commercially useful flow rate, certain colloidal or soluble impurities present in impure water will not be filtered therefrom by the microscreen. Unfortunately, many impurities affecting the purity of water with regard to its biochemical oxygen demand, chemical oxygen demand, color, pH, odor, taste, total organic content, etc., are of a size that will not be filtered.
It is known in the prior art, as disclosed in U.S. Pat. No. 3,904,518 granted to D. Hutton, et al. and entitled "Waste Water Treatment Process" and U.S. Pat. No. 4,069,148 granted to D. Hutton, et al. and entitled "Industrial Waste Water Treatment Process" and an article in Chemical Engineering on Feb. 1, 1972 at page 36 entitled "New Water--Cleanup Roles for Powdered Activated Carbon" that activated carbon and other finely divided particulate matter can be used to help remove impurities of the size not filtered by commercially usable microscreens in water purification systems. Unfortunately, these finely divided particulate matters also comprise particles of a size that will not be filtered out of impure water to which they have been added, when that impure water moves through a microscreen having a pore size that will insure a commercially useful flow rate for a water purification process. The prior art systems, thus, must employ clarifier tanks that allow the particulate matter to settle out of the water before it passes from the system.